Material selection requirements for mold making
June 14, 2019
Important steps before mold making - mold selection
When making molds for rubber products, the first consideration is the choice of mold materials. According to the quality, quantity, structure and so on of the product, the selection of the mold is determined. Mold selection is a very important part of the entire mold making process.
The mold selection needs to meet three requirements: First, the mold meets the work requirements of wear resistance, toughness, etc. Secondly, the mold meets the process requirements; again, the mold should meet the economic applicability requirements.
(1) The mold meets the working conditions
1, wear resistance
When the blank is plastically deformed in the cavity of the mold, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, which easily causes the mold to fail due to wear. Therefore, the wear resistance of the material is one of the most basic and important properties of the mold.
Hardness is a major factor affecting wear resistance. In general, the higher the hardness of the mold part, the smaller the wear amount, and the better the wear resistance. In addition, the wear resistance is also related to the type, quantity, shape, size and distribution of carbides in the material.
2, toughness
Most of the working conditions of the mold are very bad, and some often suffer from a large impact load, resulting in brittle fracture. In order to prevent the mold parts from suddenly breaking during work, the mold must have high strength and toughness. The toughness of the mold depends mainly on the carbon content, grain size and microstructure of the material.
3, fatigue fracture performance
During the working process of the mold, under the long-term effect of the cyclic stress, fatigue fracture is often caused. The form has small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture properties of a mold depend mainly on its strength, toughness, hardness, and the amount of inclusions in the material.
4, high temperature performance
When the working temperature of the mold is high, the hardness and strength are lowered, resulting in early wear of the mold or plastic deformation and failure. Therefore, the mold material should have high anti-tempering stability to ensure that the mold has high hardness and strength at the working temperature.
5, resistance to cold and heat fatigue
Some molds are in a state of repeated heating and cooling during the working process, causing the surface of the cavity to be subjected to tensile and pressure-induced stresses, causing surface cracking and spalling, increasing friction, impeding plastic deformation, and reducing dimensional accuracy, thereby resulting in The mold failed. Hot and cold fatigue is one of the main forms of hot work die failure. It should have high resistance to cold and heat fatigue.
6, corrosion resistance
Some molds, such as plastic molds, when working, due to the presence of chlorine, fluorine and other elements in the plastic, after the heat, the HCI, HF and other strong aggressive gases are resolved, eroding the surface of the mold cavity, increasing its surface roughness and aggravating wear and tear.
(2) The mold meets the process performance requirements
Mold manufacturing generally involves several processes such as forging, cutting, and heat treatment. In order to ensure the quality of the mold and reduce the production cost, the material should have good forgeability, machinability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching. Deformation cracking tendency.
1. Forgeability
It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low tendency for forging cracking and precipitation of reticulated carbides.
2, craftability
The spheroidizing annealing temperature range is wide, the annealing hardness is low, the fluctuation range is small, and the spheroidization rate is high.
3, cutting processability
Large cutting amount, low tool loss and low surface roughness.
4, oxidation, decarburization sensitivity
When heated at high temperature, the anti-oxidation energy is good, the decarburization speed is slow, and it is not sensitive to the heating medium, and the tendency to produce pitting is small.
5, hardenability
Uniform and high surface hardness after quenching.
6, hardenability
After quenching, a deep hardened layer can be obtained, which can be hardened with a mild quenching medium.
7, quenching deformation cracking tendency
The conventional quenching volume change is small, the shape is warped, the distortion is slight, and the abnormal deformation tendency is low. Conventional quench cracking has low sensitivity and is not sensitive to quenching temperature and workpiece shape.
8, grindability
The relative loss of the grinding wheel is small, the maximum amount of grinding without the burn is large, and it is not sensitive to the quality of the grinding wheel and the cooling condition, and it is not easy to cause abrasion and grinding crack.
(3) The mold meets the economic requirements
When selecting a mold, the principle of economy must be considered to reduce the manufacturing cost as much as possible. Therefore, under the premise of satisfying the performance of use, firstly, the price is lower, carbon steel can be used without alloy steel, and domestic materials can be used without imported materials.
In addition, the production and supply of the market should also be considered when selecting materials. The selected steel grades should be as small and concentrated as possible, and easy to purchase.
Knowing the knowledge of the selection of the mold can better make the advantages of the mold come into play. In order to produce better and better quality molds.
